The present invention relates to a flame-retardant silicone rubber composition or, more particularly, to a flame-retardant silicone rubber composition capable of exhibiting constant flame retardancy by the admixture of a specific flame retardant agent which is free from the problems of toxicity and adverse influences on the curing behavior of the composition as well as the mechanical properties of the cured silicone rubber thereof which is useful as an insulating material in various electric and electronic parts.
Various proposals and attempts have been made hitherto with an object to impart flame retardancy to silicone rubbers including the methods of admixture of a silicone rubber composition with a platinum compound (see, for example, Japanese Patent Publication No. 44-2591), combination of a platinum material and carbon black (see, for example, Japanese Patent Publication 47-16546) and combination of a platinum material and a fumed titanium dioxide filler (see, for example, Japanese Patent Publication 47-21826) although no satisfactory flame retardancy has yet been obtained in each of these prior art methods.
A problem accompanying the formulation of a platinum compound as a flame retardant agent is that, when the curing catalyst formulated in the silicone rubber composition is an alkyl peroxide, the flame retardancy of the silicone rubber is improved to a less extent than in the formulation with an acyl peroxide as the curing catalyst. In this regard, a proposal is made in Japanese Patent Publication 51-234302 to add a platinum compound as combined with an azo compound. This method, however, involves disadvantages that the decomposition products of the azo compound in the vulcanization may sometimes cause blistering of the cured rubber, in particular, when vulcanization is performed by the so-called hot-air vulcanization under normal pressure and that the decomposition products are toxic to cause a serious safety problem. Therefore, it is eagerly desired to develop a novel flame-retardant silicone rubber composition which is free from the above described problems and disadvantages in the silicone rubber compositions formulated with a conventional flame retardant agent of the prior art.